I have thought of a technique to increase the resolution of a POV (persistence of vision) display. In an usual POV display, the LEDs are arranged in a strip and spun in a circle. There are two limiting factors to increasing the radial resolution along the circumference of any one circular path that an LED follows. One is, depending on the speed of the POV wheel, the minimum time required (decided by the microcontroller) to change the LED's color in case of a RGB. The other factor is the LED's width, that increases the 'bleeding' of color from one pixel to the neighboring pixel if the LED changes color or brightness too fast.

If one were to fix a slit in the front of an LED, |*| <-- like so, would this help improve the resolution of the POV display; by doing this one would in effect be reducing the width of the 'pixel' along the circumference on which the led would be traversing.

Thus if one were to use a fast enough microcontroller and a narrow enough slit, one could probably obtain a very high resolution along one dimension at least.

To be clear I've not yet implemented this, and am just looking for any experienced person who can tell if this will work or not.

I have not made a POV from scratch. But I think you are right. There are some SMD LEDs that are very small. Likely on the order of 3 to 4 mm wide. If physical proximity becomes an issue, consider that the LEDs do not need to all be on a line ("spoke") from the center to the edge of the display. Instead they can be staggered on several lines or on a curved line. Then, use software to delay the information to each individual LED such that it is easy to re-create images such as a straight radial line.